place of the dead—consist of menhirs from two feet to twenty feet high, are sepulchral, and are evidently the work of the same race that built Avebury and Stonehenge, though data as to the time are wanting. Stonehenge is obviously the latest of the three, for the stones there are hewn out and fashioned with mortise blocks, etc., while Avebury and Carnac are rough and unhewn.
Coal-Mine Acids in the Schnylkill River.—It is shown in a paper by Prof. O. C. S. Carter that the Schuylkill River, above the city of Reading, is so strongly charged with sulphuric acid and sulphate of iron that it can not be used as a water supply, or, on account of its corroding boilers, for the generation of steam, and is very detrimental to fish, so that there are practically none in the river between Reading and Tamaqua. The acidity of the river is due to impurities found in coal. Before coal was mined in Pennsylvania the river, it is said, was free from acidity from its mouth to its source, and fish were found along its entire course. It is also said that the amount of acid in the Big Schuylkill from Pottsville and beyond has been decreasing since 1868, owing to the transfer of mining operations to the other side of the mountains, where the streams drain into the Susquehanna, and that the amount of sulphuric acid in the Big Schuylkill in 1885 was only one half of what it had formerly been. These statements can not be strictly verified for want of means of making comparative analyses, but are taken as true. Thanks to the decrease of acid, a few hardy catfish have found their way up to the region between Port Clinton and Pottsville, but no other fish; but even the catfish are not found in the river lower down, between Port Clinton and Reading, because of the discharge of acid waters by the Little Schuylkill at Port Clinton. The water loses its acid character in the vicinity of Reading, and neutralization is complete a short distance below. This is brought about by the pouring in of the hard, limestone waters of Maiden and Tulpehocken Creeks near Reading. At the mouths of these streams the sulphate of lime is precipitated by their action, rendering the water almost milky in appearance. In 1882, when a number of abandoned coal mines were opened and the excess of acid water was pumped into the river, there was more of it than the limestone streams could neutralize in the dry season; it passed far below the city of Reading, and hundreds of dead fish were observed floating in the river.
An Endless Source of Carbonic Acid.—Prof. E. W. Claypole's president's address at the last meeting of the American Microscopical Society—Microscopical Light in Geological Darkness—concerns the aid furnished by the microscope in geological study. Among the revelations afforded by means of this instrument is that which it has yielded, in the hands of Mr. H. C. Sorby, of Sheffield, England, of the existence of innumerable inclusions of liquid carbonic acid in the rocks. As investigation has gone on, the abundance of these bubbles has been more and more realized, and they are now found to be present "by myriads and by millions, and not in gems only, but in other crystalline minerals. In size they range between the one-thousandth and the fifty-thousandth of an inch, but they are so multitudinous as often to impart a white tint to the crystal, and many specimens of milky quartz owe their whiteness solely to the presence of these innumerable bubbles. In some of the Cornish granites the cavities make five per cent of the volume, and yield four pounds of the liquid to every ton of the rock." Mr. J. C. Ward is quoted as saying that more than a thousand millions of them might be contained easily within a cubic inch of quartz. The fact is used to cast light on the problem of the origin of the coal. Coal is derived from plants, which have extracted carbon from the carbonic acid of the atmosphere. Whence was that carbonic acid derived? It has been said that it was one of the original constituents of the atmosphere. But Professor Claypole adduces many reasons to show that all the carbonic acid represented in the coal beds could never have been in the atmosphere at one time. How, then, and whence, were the successive supplies introduced? Besides Mr. Sorby's experiments, those of Professor Tilden and others show that rocks of various kinds and in various localities yield gases, of which hydrogen and carbonic acid are the most abundant, in proportions ranging from 1.3 to 17.8 of the bulk of the rock, whence it may be inferred that these gases are occluded in most rocks. Now,
